Circuits of electronic assemblies, for example electronic control devices, generally have as their sub-assemblies or function units an input stage, a digitally operating control section, and an output/power stage. Rigid or flexible plastic PCBs, ceramic substrates and leadframes are used as substrate carriers for the components and for the electrical connection lines between the components.
The costs for the substrate carrier necessary for construction of the circuit depend on the complexity of the carrier: substrate carriers wired on one plane only and with standardized circuit path widths and spacings are superior, as regards cost, to substrate carriers wired on several planes, containing substrate through-holes, and being non-standardized as regards width and spacing of the circuit paths. The cost factor is becoming increasingly influential the more the selected substrate technology approaches its technological boundaries. This generally occurs when the design of the circuit is heavily affected by space restrictions.
Particularly in those cases in which construction of the above digital control section requires the interconnection of several digital ICs with a large number of pins, either a large amount of space or a sophisticated technology is required on the substrate carrier purely for the circuit path connection--quite apart from the disproportionately high space requirement of the housings used in relation to the semiconductor chip proper.